1. Field of the Invention
The present invention relates to a lens for projection and a projection-type display apparatus. For example, the present invention relates to a lens for projection appropriately usable to magnify and project rays including video image information from a light valve onto a screen, and also so a projection-type display apparatus using the lens for projection.
2. Description of the Related Art
In recent years, a market for projection-type display apparatuses greatly expanded as personal computers became widely used. As a light valve for performing light modulation, a transmission-type or reflection-type liquid crystal display device, a DMD (Digital Micromirror Device: registered trademark), in which micromirrors are regularly arranged, and the like are known projection-type display apparatus using such a light valve needs to have excellent convenient characteristics and installation characteristics, small size and light weight, and a small F-number. Therefore, a lens for projection to be mounted on the projection-type display apparatus also needs to have a wide angle of view, small size and light weight, and to have a small F-number, and to be at low cost, and to consist of a small number of lenses.
In a projection-type display apparatus using light valves, a lens for projection needs a sufficient length of back focus to arrange, toward a reduction side of the lens for projection, a color combination member for combining modulated light, which has been modulated by a different light valve for each color, a separation member for separating projection light and illumination light from each other, and the like. As a lens for projection consisting of a small number of lenses and having a relatively long back focus, lenses for projection disclosed, for example, in Japanese Unexamined Patent Publication No. 9(1997)-145998 (Patent Document 1), Japanese Unexamined Patent Publication No. 2 (1990)-184809 (Patent Document 2), Japanese Unexamined Patent Publication NO. 2000-039555 (Patent Document 3) and Japanese Unexamined Patent Publication No. 2002-341242 (Patent Document 4) are known. Patent Document 1 discloses a lens system consisting of six lenses of a positive lens, a positive lens, a negative lens, a negative lens, a positive lens and a positive lens arranged in this order from a magnification side. Each of Patent Documents 2 and 3 discloses a lens system consisting of six lenses of a positive lens, a negative lens, a negative lens, a positive lens, a positive lens and a positive lens arranged in this order from a magnification side. Patent Document 4 discloses, as Example 8, a lens system consisting of six lenses of a positive lens, a negative lens, a positive lens, a negative lens, a positive lens and a positive lens arranged in this order from a magnification side.